Gyrostrea delettrei ( Coquand, 1862 )

Musavu Moussavou, Benjamin, 2017, Systematics, palaeoecology and taphonomy of Turonian oysters from the northern Gabon Coastal Basin, Geodiversitas 39 (2), pp. 213-224 : 218

Gyrostrea delettrei ( Coquand, 1862)

( Fig. 4 G-N)

Ostrea delettrei Coquand, 1862 : 224, pl. 18, figs 1-7. — Fourtau 1917: 34; pl. 1, figs 1-4.

Exogyra delettrei – Pervinquière 1912 : 186, pl. 12, figs 18,?19. — Trevisan 1937: 74, pl. 5, figs 5-10.

Crassostrea (Gyrostrea) delettrei tarfayensis – Freneix 1972: 98, pl. 8, figs 5-8; pl. 9, figs 1-7.

Gyrostrea delettrei – El-Sheikh et al. 1998: pl. 1, fig. B. — Ayoub-Hannaa 2011: 92, pl. 8, figs 3, 4.

MATERIAL. — 10 specimens (MDG/LBV/Lm-12.1 to Lm-12.10).

OCCURRENCE. — This species has been recorded from Cenomanian to Turonian of North Africa ( Pervinquière 1912; Freneix 1972; El- Sheikh et al. 1998; Ayoub-Hannaa 2011), Italy ( Trevisan 1937). In Gabon this is the first record.

DESCRIPTION

Shell is medium to large, inequivalve, inequilateral, elongated, subtrigonal to elliptical shape in outline. Left and right valves are respectively convex and flat. Umbo is small and opisthogyrate. Anterior margin curved into approximately semicircular shape. Posterior margin is straight or curved. Ventral margin is evenly rounded. Attachment area is rounded and large. LV ornamentation consists of radial and continuous ribs towards umbonal area where are crossing by concentric growth lamellae. Towards ventral margin, ornamentation consists only of widely spaced imbricating concentric growth lamellae separated by wide interspaces. RV is ornamented by concentric fine growth squamae.

REMARK

The specimens of Gyrostrea delettrei ( Coquand, 1862) from Gabon Coastal Basin show some similarity to Ostrea roachensis ( Fourtau 1917: 50, pl. 3, fig. 1), but differ in having a variable size shape, size of the attachment area.

Figures

FIG. 4. — A-D, Ostrea sp. D: A, B, MDG/LBV/Lm-33.1; C, D, MDG/LBV/Lm-33.2; E, Ostrea sp. C MDG/LBV/Lm-32.1; F, Gyrostrea sp. B MDG/LBV/Lm-14; G-N, Gyrostrea delettrei (Coquand,1862);G, H, MDG/LBV/Lm-12.1;I, J, MDG/LBV/Lm-12.2;K, L, MDG/LBV/Lm-12.3,M-N.MDG/LBV/Lm-12.4;O-R, Ostrea sp.B;O, P, MDG/LBV/Lm-31.1;Q, R, MDG/LBV/Lm-31.2;S-U, Ostrea sp.A,S-T.MDG/LBV/Lm-15.1;U, MDG/LBV/Lm-15.2.Scale bar:1 cm.